Felted, open-cell urethane foam is employed in ink jet ink cartridges as a holder or wick for the ink. The foam fills the ink reservoir and ink in the reservoir is virtually entirely contained in the cells of the foam. This provides proper flow and metering of the ink to ejection chambers of the ink cartridge. Ink is ejected from small holes, termed nozzles, in the cartridge. At least for inks ejected by heating at the chamber to form vapor which propels the ink, the presence of residues typical of those from chemical degradation of urethane tends to clog the nozzles.
Prior to this invention foam used for the ink delivery in an ink jet cartridge contained levels of non-volatile residue in the range of 0.5% to above 3.0% by weight of the total weight. This residue consists of: 1) low molecular weight urethane resulting from the chain termination during foaming and from degradation of the urethane linkages during manufacture of the foam and 2) remnants of surfactant used as an ingredient in the foam formulation. Such residues deposit on the plate having the nozzles to cause clogs and other operational failures.
The prior art recognizes the existence of the residues and teaches removal of the residues by washing operations (U.S. Pat. Nos. 4,824,487 to Heffernan and 5,182,579 to Haruta et al). The problems with residues have remained, although reduced by the cleaning. Cleaning also has the disadvantages of: 1) adding cost and 2) requiring disposal and control of contaminated solvent from the cleaning process.
The foregoing U.S. Pat. Nos. 5,182,579 also reduces from previous levels the temperature during the compression between heated plates. This reduces the residues somewhat, but not enough under all conditions to eliminate problems with residue.